Glass Substrate for Information Recording Medium and Information Recording Medium

ABSTRACT

A glass substrate for information recording medium, said glass substrate being composed of an alminosilicate glass containing 60-75% by mass of SiO 2 , 5-18% by mass of Al 2 O 3 , 3-10% by mass of Li 2 O, 3-15% by mass of Na 2 O and 0.5-8% by mass of ZrO 2  relative to the entire glass components. The glass substrate for information recording medium contains neither As (arsenic) nor Sb (antimony), while containing at least one polyvalent element selected from the group consisting of V (vanadium), Mn (manganese), Ni (nickel), Nb (niobium), Mo (molybdenum), Sn (tin), Ce (cerium), Ta (tantalum) and Bi (bismuth). The molar ratio of the total amount of the polyvalent elements to the amount of ZrO 2  is within the range of 0.05-0.50.

TECHNICAL HELD

The present invention relates to a glass substrate for an informationrecording medium such as a magnetic disk and an information recordingmedium using the same, and more specifically to a glass substrate for aninformation recording medium made of aluminosilicate glass and aninformation recording medium using the same.

BACKGROUND

Of information recording media having a recording layer utilizingmagnetic, optical, or magneto-optical properties, magnetic disks areavailable as typical media. Conventionally, as magnetic disk substrates,aluminum substrates have been widely used. However, over recent years,with the demand for the reduction of magnetic head floating amount forrecording density enhancement, glass substrates have been increasinglyused, which glass substrates exhibit superior surface flatness toaluminum substrates and have less surface defects. Of these, preferablyused are glass substrates formed of aluminosilicate glass capable ofstrengthening substrates by chemical strengthening treatment by ionexchange, because of their enhanced impact resistance and vibrationresistance.

In such a glass substrate for an information recording medium, to becapable of high density recording with reduced surface defects, it isnecessary that gas bubbles generated in the melting process of glass areallowed to be present in a glass substrate at as lowest level aspossible. Conventionally, a method has been commonly employed in whichAs₂O₃ and Sb₂O₃ are contained in a glass component as fining agents,whereby gas bubbles in molten glass are removed (clarified) (forexample, refer to Patent Document 1).

However, since As₂O₃ and Sb₂O₃ are toxic, from the environmental andhealth viewpoints, a tendency to regulate the usage thereof is beingwidespread. Therefore, studies have been made to realize a method toremove gas bubbles in the molten glass without using As₂O₃ or Sb₂O₃serving as fining agents is studied (for example, Patent Document 2),and proposed is a method to remove gas bubbles by depressurizing moltenglass.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Unexamined Japanese Patent Application    Publication No. 8-321034-   Patent Document 2: Patent Document 1: Unexamined Japanese Patent    Application Publication No. 2000-128549

BRIEF DESCRIPTION OF THE INVENTION Problems to be Solved by theInvention

However, according to the method described in Patent Document 2, therehave been such problems that a complex process and a specialdecompression degassing apparatus are required and also a glasscomponent tends to be changed by volatilization of the glass componentwith pressure reduction.

In view of the above technological problems, the present invention wasconceived. An object of the present invention is to provide a glasssubstrate for an information recording medium with sufficiently removedgas bubbles in which neither As (arsenic) nor Sb (antimony) element iscontained; and an information recording medium using the same.

Means to Solve the Problems

To solve the above problems, the present invention has the followingfeatures.

Item 1. A glass substrate for an information recording medium made ofaluminosilicate glass containing 60% to 75% by mass of SiO₂, 5% to 18%by mass of Al₂O₃, 3% to 10% by mass of Li₂O, 3% to 15% by mass of Na₂O,and 0.5% to 8% by mass of ZrO₂ with respect to whole glass components,comprising:

neither As (arsenic) element nor Sb (antimony) element;

at least one type of polyvalent element selected from the groupconsisting of V (vanadium), Mn (manganese), Ni (nickel), Nb (niobium),Mo (molybdenum), Sn (tin), Ce (cerium), Ta (tantalum), and Bi (bismuth),

wherein a molar ratio of a whole amount of the polyvalent element to theZrO₂, which is (the whole amount of the polyvalent element)/ZrO₂, iswithin a range of 0.05 to 0.50.

Item 2. The glass substrate for an information recording medium of item1, comprising:

at least one polyvalent element selected from the group consisting of V(vanadium), Mn (manganese), Sn (tin), and Ce (cerium).

Item 3. The glass substrate for an information recording medium of item1 or 2, wherein a total content of the polyvalent element is 1% by massor less with respect to the whole glass components,

where each of the polyvalent elements is converted in terms of thefollowing oxides: V₂O₅ for V; MnO₂ for Mn; Ni₂O₅ for Ni; Nb₂O₅ for Nb;MoO₃ for Mo; SnO₂ for Sn; CeO₂ for Ce; Ta₂O₅ for Ta; and Bi₂O₃ for Bi.

Item 4. The glass substrate for an information recording medium of anyone of items 1 to 3, wherein the polyvalent element is added as finingagent made of oxide, hydroxide, or carbonate.

Item 5. The glass substrate for an information recording medium of anyone of items 1 for 4, wherein the glass substrate for an informationrecording medium is chemically strengthened by ion exchange.

Item 6. An information recording medium, comprising:

a recording layer provided on the glass substrate for an informationrecording medium of any one of items 1 to 5.

Advantages of the Invention

According to the present invention, since predetermined polyvalentelements made of oxides functioning as fining agents in glass arecontained at a molar ratio of a predetermined range to ZrO₂ in the glasscomponents, clarification reaction due to the valence change of thepolyvalent elements can effectively function. Therefore, without As(arsenic) or Sb (antimony) element, a glass substrate for an informationrecording medium with sufficiently removed gas bubbles can be obtained.

PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention will now be described indetail.

(Glass Substrate for an Information Recording Medium)

The glass substrate for an information recording medium of the presentinvention is made of an aluminosilicate glass containing 60-75% by massof SiO₂, 5-18% by mass of Al₂O₃, 3-10% by mass of Li₂O, 3-15% by mass ofNa₂O, and 0.5-8% by mass of ZrO₂ with respect to the total glasscomponents. Therefore, chemical strengthening treatment by ion exchangecan be applied thereto, whereby enhanced impact resistance and vibrationresistance can be ensured. The reason why each component was regulatedin the above range is as follows:

SiO₂ is a critical component to form a network structure of glass andsignificantly contributes to chemical resistance. When the content ofSiO₂ is less than 60% by mass, chemical resistance may be lower. Incontrast, in the case of more than 75% by mass, melting temperature isexcessively high. Therefore, the content of SiO₂ needs to fall in arange of 60-75% by mass. In this range, a range of 60-71% by mass ispreferable.

Al₂O₃ is a critical component to form a network structure together withSiO₂, functioning to enhance not only chemical resistance but also ionexchange performance. When the content of Al₂O₃ is less than 5% by mass,chemical resistance and ion exchange performance may be lower. Incontrast, in the case of more than 18% by mass, devitrificationresistance is lower. Therefore, the content of Al₂O₃ needs to fall in arange of 5-18% by mass. In this range, a range of 9-14% by mass ispreferable.

LiO₂ is a necessary component to carry out chemical strengtheningtreatment by ion exchange. In the chemical strengthening treatment, Li⁺ions in glass are ion-exchanged with Na⁺ ions or K⁺ ions contained in achemical strengthening treatment liquid, whereby a glass substrate isstrengthened. When the content of LiO₂ is less than 3% by mass, this ionexchange performance is lower. In contrast, in the case of more than 10%by mass, devitrification resistance and chemical resistance are lower.Therefore, the content of LiO₂ needs to be 3-10% by mass. In this range,a range of 4-6% by mass is preferable.

Na₂O is a necessary component to carry out chemical strengtheningtreatment by ion exchange. In the chemical strengthening treatment, Na⁺ions in glass are ion-exchanged with K⁺ ions contained in a chemicalstrengthening treatment liquid, whereby a glass substrate isstrengthened. When the content of Na₂O is less than 3% by mass, this ionexchange performance is decreased and also devitrification resistance islower. In contrast, in the case of more than 15% by mass, chemicalresistance is decreased. Therefore, the content of Na₂O needs to be3-15% by mass. In this range, a range of 6-10% by mass is preferable.

ZrO₂ is a necessary component to enhance chemical resistance. When thecontent of ZrO₂ is less than 0.5% by mass, chemical resistance is lower.In contrast, in the case of more than 8% by mass, devitrificationresistance is lower. Therefore, the content of ZrO₂ needs to be 0.5-8%by mass. In this range, a range of 1-7% by mass is preferable.

Either As₂O₃ or Sb₂O₃ is not contained. Herein, “being not contained”refers to exclude intentional addition of those elements as rawmaterials of glass. Allowable is a trace amount contained to the extentthat they are inevitably contained as impurities in raw materials ofother components.

The investigation results obtained by the present inventors made itclear that in a glass substrate containing each of the above components,predetermined polyvalent elements made of oxide functioning as finingagents in glass were contained at a molar ratio in a predetermined rangeto ZiO₂ in the glass components, whereby without As (arsenic) or Sb(antimony) element, gas bubbles in the glass were sufficiently removed.Namely, the glass substrate for an information recording medium of thepresent invention contains at least one polyvalent element selected fromthe group consisting of V (vanadium), Mn (manganese), Ni (nickel), Nb(niobium), Mo (molybdenum), Sn (tin), Ce (cerium), Ta (tantalum), and Bi(bismuth). The molar ratio of the total amount of these polyvalentelements to the amount of ZiO₂ in the glass components, which is (thetotal amount of the polyvalent elements)/ZiO₂, falls in a range of0.05-0.50.

The reason why gas bubbles can be sufficiently removed as describedabove when predetermined polyvalent elements are contained at a molarratio in a predetermined range to ZrO₂ in the glass components isbasically considered as follows.

In general, a fining agent having an oxide form in glass contributes toremoving (clarifying) gas bubbles present in molten glass by thefollowing two functions:

(a) The first one of the functions is a function to generate gas inmolten glass in the process of raising the temperature of the moltenglass. Gas bubbles in the molten glass move upward by the buoyancythereof to reach the surface of the molten glass, resulting in burstingand disappearance. Herein, the ascending velocity of the gas bubbles inmolten glass largely depend on the size of the gas bubbles. Large gasbubbles relatively easily reach the surface due to large ascendingvelocity thereof. However, small gas bubbles have small ascendingvelocity, whereby an extremely long time is required to reach thesurface. In the process of raising the temperature of molten glass, gasis generated from a fining agent, whereby gas bubbles in the moltenglass grow larger and then the ascending velocity of the gas bubbles isincreased, resulting in accelerating the disappearance of the gasbubbles.

For example, when Ce is contained as a polyvalent element, hightemperature allows the reaction of Equation 1 described below to moverightward, whereby O₂ gas is generated in molten glass. Due to thethus-generated O₂ gas, gas bubbles in the molten glass grow larger anddisappear at the surface of the molten glass.

$\begin{matrix}{{2\; {CeO}_{2}} = {{{Ce}_{2}O_{3}} + {\frac{1}{2}O_{2}}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

(b) The second one of the functions is a function to absorb gas presentin molten glass in the process of decreasing the temperature of themolten glass. For example, when Ce is contained as a polyvalent element,in the process of decreasing the temperature, the reaction of Equation 1moves left. Thereby, O₂ gas in the molten glass is absorbed and then gasbubbles shrink and disappear.

In order to sufficiently remove gas bubbles in molten glass as describedabove, it is necessary that the generation and absorption of gas by thevalence change of a polyvalent element functioning as a fining agentmade of oxide are effectively carried out. The present inventorsconducted diligent investigations with respect to the valence change ofa polyvalent element in molten glass, and then found that the reactionof the valence change of a polyvalent element functioning as a finingagent made of oxide was largely affected by the redox reaction of othermetal ions, specifically Zr ions coexisting in molten glass. Then,investigations were further conducted, whereby it was found that in analuminosilicate glass having predetermined components, when the molarratio of the total amount of the above polyvalent elements to the amountof ZrO₂, which is (the total amount of the polyvalent elements)/ZrO₂,fell in a range of 0.05-0.50, clarification reaction by the valencechange of the polyvalent elements was effectively performed.

As the polyvalent elements, at least one type selected from the groupconsisting of V (vanadium), Mn (manganese), Ni (nickel), Nb (niobium),Mo (molybdenum), Sn (tin), Ce (cerium), Ta (tantalum), and Bi (bismuth).Only one type of polyvalent element may be contained alone, or two ormore types ofpolyvalent elements may be contained. Of these, V(vanadium), Mn (manganese), Sn (tin), and Ce (cerium) are specificallypreferable since they can effectively remove gas bubbles.

When the molar ratio of the total amount of the polyvalent elements tothe amount of ZrO₂, which is (the total amount of the polyvalentelements)/ZrO₂, falls outside a predetermined range, clarificationreaction by the valence change is inadequate, whereby it becomesdifficult to sufficiently remove gas bubbles in molten glass.Accordingly, the molar ratio to ZrO₂ needs to fall in a range of0.05-0.50, more preferably in a range of 0.1-0.4.

Further, from the viewpoint of sufficiently expressing clarificationeffects with no decrease in devitrification resistance, the totalcontent of the polyvalent elements in terms of their oxides describedbelow is preferably at most 1% by mass with respect to the total glasscomponents. Herein, V, Mn, Ni, Nb, Mo, Sn, Ce, Ta, and Bi are consideredin terms of V₂O₅, MnO₂, Ni₂O₃, Nb₂O₅, MoO₃, SnO₂, CeO₂, Ta₂O₅, Bi₂O₃,respectively.

Incidentally, these polyvalent elements function as fining agents madeof oxides in molten glass. However, raw materials for them are notlimited to the form of oxides and may be used through appropriateselection from raw materials of well-known forms such as single metal,hydroxides, sulfates, or carbonates. Of these, from the viewpoint ofeasy handling, it is more preferable to add them as finishing agentsmade of oxides, hydroxides, or carbonates.

Further, the shape of a glass substrate is not specifically limited.However, a disk-shaped substrate having a central hole is common. Thesize and thickness of a glass substrate are not specifically limited.For example, the outer diameter is 2.5 inches, 1.8 inches, 1 inch, or0.8 inch and the thickness is 1 mm, 064 mm, or 0.4 mm.

(Production Method of a Glass Substrate for an Information RecordingMedium)

As described above, in the glass substrate for an information recordingmedium of the present invention, gas bubbles can be sufficiently removedby the function of predetermined fining agents. Thereby, neither acomplex process nor a special apparatus for production is required,whereby production can be carried out using a well-known, commonproduction method.

Usually, it is common that a blank material as the base of a glasssubstrate for an information recording medium is prepared andthereafter, production is carried out in processes such as inner andouter circumference processing, grinding and polishing processing,chemical strengthening treatment, and cleaning. With regard to thepreparation of the blank material, a method of preparation by pressmolding of molten glass and a method of preparation by cutting sheetglass are known. The inner and outer circumference processing is aprocess to carry out boring processing of a central hole, grindingprocessing to form the shape of the inner and outer circumferences andto ensure dimensional accuracy, and polishing process of the inner andouter circumferences. The grinding and polishing processing is a processto carry out grinding processing and polishing processing to satisfy theflatness and the surface roughness of a surface on which a recordinglayer is formed. Usually, the process is frequently carried out bydividing into some stages such as coarse grinding processing, finegrinding processing, primary polishing processing, and secondarypolishing processing. The chemical strengthening treatment is a processto immerse a glass substrate in a chemical strengthening treatmentliquid to strengthen the same. And, the cleaning is a process to removeabrasives remaining on the surface of a glass substrate and foreignsubstances such as a chemical strengthening treatment liquid.

In particular, since the glass substrate for an information recordingmedium of the present invention is made of aluminosilicate glasscontaining predetermined glass components, enhanced impact resistanceand vibration resistance can be ensured by chemical strengtheningtreatment. The chemical strengthening treatment is carried out by an ionexchange method in which a glass substrate is immersed in a heatedchemical strengthening treatment liquid, whereby lithium ions and sodiumions being components of the glass substrate are exchanged with ionssuch as sodium ions and potassium ions having larger ion radiuses thanthese ions. Strain produced by the ion radius difference generatescompressive stress in the region where the ions have been exchanged,whereby the surface of the glass substrate is strengthened.

As the chemical strengthening treatment liquid, a molten salt containingsodium ions or potassium ions is commonly used. For example, a nitrate,a carbonate, and a sulfate of sodium or potassium, and a mixed meltedsalt thereof are cited. Of these, from the viewpoint of low meltingpoint and being able to prevent the deformation of a glass substrate, amixed molten salt of sodium nitrate (NaNO₃) and potassium nitrate (KNO₃)is preferably used.

(Information Recording Medium)

An information recording medium can be produced by forming at least arecording layer on the above glass substrate for an informationrecording medium. The recording medium is not specifically limited, andvarious types of recording layers utilizing magnetic, optical, ormagneto-optical properties are usable. An information recording medium(a magnetic disk), employing a magnetic layer as a recording layer, isespecially suitable for production.

Magnetic materials used for such a magnetic layer are not specificallylimited, and well-known materials can be appropriately selected andused. However, to realize enhanced retention power, a Co-based alloycontaining Co exhibiting large crystal anisotropy as the main componentis suitable. In particular, listed are CoPt, CoCr, CoNi, CoNiCr, CoCrTa,CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, and CoCrPtSiO. Further,employable is a multi-layer structure (for example, CoPtCr/CrMo/CoPtCror CoCrPtTa/CrMo/CoCrPtTa) to reduce noise by dividing a magnetic layerby a non-magnetic material (for example, Cr, CrMo, or CrV).

As the magnetic layer, other than the above Co-based materials,ferrite-based or iron-rare-earth-based materials, or granular materialshaving a structure in which magnetic particles of Fe, Co, CoFe, orCoNiPt are dispersed in a non-magnetic film formed of SiO₂ or BN arealso usable. The magnetic layer may employ either one of an in-planetype and a vertical type recording format.

As a formation method for a magnetic layer, any appropriate well-knownmethod is usable. For example, cited are a method to spin-coat with athermally curable resin, in which magnetic particles are dispersed, on aglass substrate for an information recording medium, a sputteringmethod, and an electroless plating method. From the viewpoint of thinnerfilm and higher density realization of a magnetic layer, the sputteringmethod or the electroless plating method is preferable.

For a magnetic disk, an underlayer is further provided as appropriate.As materials for the underlayer, non-magnetic metals such as Cr, Mo, Ta,Ti, W, V, B, Al, and Ni are listed. When a magnetic layer contains Co asthe main component, from the viewpoint of magnetic characteristicenhancement, a material for the underlayer is preferably single Cr or Cralloy. Further, the underlayer is not limited to a monolayer and mayhave a multi-layer structure in which layers formed of the same ordifferent materials are layered. For example, Cr/Cr, Cr/CrMo, Cr/CrV,NiAl/Cr, NiAl/CrMo, and NiAl/CrV are cited.

Further, the surface of a magnetic layer may be provided with aprotective layer to prevent abrasion and corrosion of the magneticlayer. As the protective layer, for example, a Cr layer, a Cr alloylayer, a carbon layer, a hydrogenated carbon layer, a ZrO₂ layer, and anSiO₂ layer are cited. The protective layer may be a monolayer or have amultilayer structure containing layers of the same kind or differentkinds. Such a protective layer can continuously be formed using aninline-type sputtering apparatus, together with the underlayer and themagnetic layer. Further, when forming a protective layer of SiO₂ layeredon a Cr layer is formed, the SiO₂ layer may be formed in such a mannerthat a solution of tetraalkoxysilane diluted with an alcohol-basedsolvent and therein in which colloidal silica fine particles aredispersed, is coated on a Cr layer and then baked.

Still further, the surfaces of the magnetic layer and the protectivelayer may be provided with a lubricating layer to improve slippingproperties of a magnetic head. As the lubricating layer, examplesinclude a layer of a liquid lubricant containing perfluoropolyether(PFPE) applied and then subjected to a thermal treatment as appropriate.

EXAMPLES

Examples carried out to confirm the advantages of the present inventionwill now be described without limiting the present invention thereto.

Raw materials were blended according to the glass components shown inTable 1-Table 10 described below. As fining agents, V₂O₅ (Table 1), MnO₂(Table 2), SnO₂ (fable 3), CeO₂ (Table 4), Ni₂O₃ (Table 5), Nb₂O₅ (Table6), MoO₃ (Table 7), Ta₂O₅ (Table 8), Bi₂O₃ (Table 9), and a mixture ofCeO₂ and SnO₂ (Table 10) each were used. Herein, neither As nor Sb wasnot contained in any fining agent above.

TABLE 1 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of GasDevitrifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.1-1 Comparative 70.84 10.00 5.00 7.00 7.00 V₂O₅ 0.16 (V/ZrO₂) = 0.03 31A Example No. 1-2 Example 70.74 10.00 5.00 7.00 7.00 V₂O₅ 0.26 (V/ZrO₂)= 0.05 0 A No. 1-3 Example 70.13 9.90 4.90 6.90 6.90 V₂O₅ 1.27 (V/ZrO₂)= 0.25 0 B No. 1-4 Example 69.28 9.70 4.90 6.80 6.80 V₂O₅ 2.52 (V/ZrO₂)= 0.50 0 B No. 1-5 Comparative 68.89 9.70 4.80 6.80 6.80 V₂O₅ 3.01(V/ZrO₂) = 0.60 21 B Example No. 1-6 Comparative 62.79 14.00 6.00 10.007.00 V₂O₅ 0.21 (V/ZrO₂) = 0.04 40 A Example No. 1-7 Example 62.74 14.006.00 10.00 7.00 V₂O₅ 0.26 (V/ZrO₂) = 0.05 0 A No. 1-8 Example 62.2313.80 5.90 9.90 6.90 V₂O₅ 1.27 (V/ZrO₂) = 0.25 0 B No. 1-9 Example 61.5813.60 5.80 9.70 6.80 V₂O₅ 2.52 (V/ZrO₂) = 0.50 0 B No. 1-10 Comparative61.09 13.60 5.80 9.70 6.80 V₂O₅ 3.01 (V/ZrO₂) = 0.60 25 B Example

TABLE 2 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of GasDevitrifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.2-1 Comparative 70.85 10.00 5.00 7.00 7.00 MnO₂ 0.15 (Mn/ZrO₂) = 0.03 31A Example No. 2-2 Example 70.75 10.00 5.00 7.00 7.00 MnO₂ 0.25 (Mn/ZrO₂)= 0.05 0 A No. 2-3 Example 70.18 9.90 4.90 6.90 6.90 MnO₂ 1.22 (Mn/ZrO₂)= 0.25 0 B No. 2-4 Example 69.29 9.80 4.90 6.80 6.80 MnO₂ 2.41 (Mn/ZrO₂)= 0.50 0 B No. 2-5 Comparative 68.92 9.70 4.90 6.80 6.80 MnO₂ 2.88(Mn/ZrO₂) = 0.60 21 B Example No. 2-6 Comparative 62.80 14.00 6.00 10.007.00 MnO₂ 0.20 (Mn/ZrO₂) = 0.04 40 A Example No. 2-7 Example 62.75 14.006.00 10.00 7.00 MnO₂ 0.25 (Mn/ZrO₂) = 0.05 0 A No. 2-8 Example 62.2813.80 5.90 9.90 6.90 MnO₂ 1.22 (Mn/ZrO₂) = 0.25 0 B No. 2-9 Example61.39 13.70 5.90 9.80 6.80 MnO₂ 2.41 (Mn/ZrO₂) = 0.50 0 B No. 2-10Comparative 61.22 13.60 5.80 9.70 6.80 MnO₂ 2.88 (Mn/ZrO₂) = 0.60 25 BExample

TABLE 3 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of AirDiversifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.3-1 Comparative 70.74 10.00 5.00 7.00 7.00 SnO₂ 0.26 (Sn/ZrO₂) = 0.03 32A Example No. 3-2 Example 70.57 10.00 5.00 7.00 7.00 SnO₂ 0.43 (Sn/ZrO₂)= 0.05 0 A No. 3-3 Example 69.40 9.80 4.90 6.90 6.90 SnO₂ 2.10 (Sn/ZrO₂)= 0.25 0 B No. 3-4 Example 68.09 9.60 4.80 6.70 6.70 SnO₂ 4.11 (Sn/ZrO₂)= 0.50 0 B No. 3-5 Comparative 67.41 9.50 4.80 6.70 6.70 SnO₂ 4.89(Sn/ZrO₂) = 0.60 29 B Example No. 3-6 Comparative 62.66 14.00 6.00 10.007.00 SnO₂ 0.34 (Sn/ZrO₂) = 0.04 43 A Example No. 3-7 Example 62.67 13.906.00 10.00 7.00 SnO₂ 0.43 (Sn/ZrO₂) = 0.05 0 A No. 3-8 Example 61.6013.70 5.90 9.80 6.90 SnO₂ 2.10 (Sn/ZrO₂) = 0.25 0 B No. 3-9 Example60.39 13.40 5.80 9.60 6.70 SnO₂ 4.11 (Sn/ZrO₂) = 0.50 0 B No. 3-10Comparative 59.91 13.30 5.70 9.50 6.70 SnO₂ 4.89 (Sn/ZrO₂) = 0.60 36 BExample

TABLE 4 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of GasDevitrifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.4-1 Comparative 70.70 10.00 5.00 7.00 7.00 CeO₂ 0.30 (Ce/ZrO₂) = 0.03 26A Example No. 4-2 Example 70.51 10.00 5.00 7.00 7.00 CeO₂ 0.49 (Ce/ZrO₂)= 0.05 0 A No. 4-3 Example 69.31 9.80 4.90 6.80 6.80 CeO₂ 2.39 (Ce/ZrO₂)= 0.25 0 B No. 4-4 Example 67.64 9.50 4.80 6.70 6.70 CeO₂ 4.66 (Ce/ZrO₂)= 0.50 0 B No. 4-5 Comparative 67.16 9.40 4.70 6.60 6.60 CeO₂ 5.54(Ce/ZrO₂) = 0.60 19 B Example No. 4-6 Comparative 62.71 13.90 6.00 10.007.00 CeO₂ 0.39 (Ce/ZrO₂) = 0.04 33 A Example No. 4-7 Example 62.61 13.906.00 10.00 7.00 CeO₂ 0.49 (Ce/ZrO₂) = 0.05 0 A No. 4-8 Example 61.4113.70 5.90 9.80 6.80 CeO₂ 2.39 (Ce/ZrO₂) = 0.25 0 B No. 4-9 Example60.14 13.30 5.70 9.50 6.70 CeO₂ 4.66 (Ce/ZrO₂) = 0.50 0 B No. 4-10Comparative 59.56 13.20 5.70 9.40 6.60 CeO₂ 5.54 (Ce/ZrO₂) = 0.60 29 BExample

TABLE 5 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of GasDevitrifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.5-1 Comparative 70.86 10.00 5.00 7.00 7.00 Ni₂O₃ 0.14 (Ni/ZrO₂) = 0.0334 A Example No. 5-2 Example 70.77 10.00 5.00 7.00 7.00 Ni₂O₃ 0.23(Ni/ZrO₂) = 0.05 3 A No. 5-3 Example 70.24 9.90 4.90 6.90 6.90 Ni₂O₃1.16 (Ni/ZrO₂) = 0.25 1 B No. 5-4 Example 69.40 9.80 4.90 6.80 6.80Ni₂O₃ 2.30 (Ni/ZrO₂) = 0.50 1 B No. 5-5 Comparative 69.06 9.70 4.90 6.806.80 Ni₂O₃ 2.74 (Ni/ZrO₂) = 0.60 20 B Example No. 5-6 Comparative 62.8114.00 6.00 10.00 7.00 Ni₂O₃ 0.19 (Ni/ZrO₂) = 0.04 35 A Example No. 5-7Example 62.77 14.00 6.00 10.00 7.00 Ni₂O₃ 0.23 (Ni/ZrO₂) = 0.05 4 A No.5-8 Example 62.34 13.80 5.90 9.90 6.90 Ni₂O₃ 1.16 (Ni/ZrO₂) = 0.25 1 BNo. 5-9 Example 61.50 13.70 5.90 9.80 6.80 Ni₂O₃ 2.30 (Ni/ZrO₂) = 0.50 2B No. 5-10 Comparative 61.36 13.60 5.80 9.70 6.80 Ni₂O₃ 2.74 (Ni/ZrO₂) =0.60 31 B Example

TABLE 6 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of GasDevitrifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.6-1 Comparative 70.77 10.00 5.00 7.00 7.00 Nb₂O₅ 0.23 (Nb/ZrO₂) = 0.0328 A Example No. 6-2 Example 70.62 10.00 5.00 7.00 7.00 Nb₂O₅ 0.38(Nb/ZrO₂) = 0.05 4 A No. 6-3 Example 69.65 9.80 4.90 6.90 6.90 Nb₂O₅1.85 (Nb/ZrO₂) = 0.25 2 B No. 6-4 Example 68.56 9.60 4.80 6.70 6.70Nb₂O₅ 3.64 (Nb/ZrO₂) = 0.50 2 B No. 6-5 Comparative 67.87 9.60 4.80 6.706.70 Nb₂O₅ 4.33 (Nb/ZrO₂) = 0.60 27 B Example No. 6-6 Comparative 62.7014.00 6.00 10.00 7.00 Nb₂O₅ 0.30 (Nb/ZrO₂) = 0.04 38 A Example No. 6-7Example 62.72 13.90 6.00 10.00 7.00 Nb₂O₅ 0.38 (Nb/ZrO₂) = 0.05 3 A No.6-8 Example 61.85 13.70 5.90 9.80 6.90 Nb₂O₅ 1.85 (Nb/ZrO₂) = 0.25 3 BNo. 6-9 Example 60.76 13.50 5.80 9.60 6.70 Nb₂O₅ 3.64 (Nb/ZrO₂) = 0.50 2B No. 6-10 Comparative 60.27 13.40 5.70 9.60 6.70 Nb₂O₅ 4.33 (Nb/ZrO₂) =0.60 27 B Example

TABLE 7 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of GasDevitrifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.7-1 Comparative 70.75 10.00 5.00 7.00 7.00 MoO₃ 0.25 (Mo/ZrO₂) = 0.03 34A Example No. 7-2 Example 70.59 10.00 5.00 7.00 7.00 MoO₃ 0.41 (Mo/ZrO₂)= 0.05 5 A No. 7-3 Example 69.50 9.80 4.90 6.90 6.90 MoO₃ 2.00 (Mo/ZrO₂)= 0.25 4 B No. 7-4 Example 68.27 9.60 4.80 6.70 6.70 MoO₃ 3.93 (Mo/ZrO₂)= 0.50 5 B No. 7-5 Comparative 67.62 9.50 4.80 6.70 6.70 MoO₃ 4.68(Mo/ZrO₂) = 0.60 37 B Example No. 7-6 Comparative 62.67 14.00 6.00 10.007.00 MoO₃ 0.33 (Mo/ZrO₂) = 0.04 39 A Example No. 7-7 Example 62.69 13.906.00 10.00 7.00 MoO₃ 0.41 (Mo/ZrO₂) = 0.05 5 A No. 7-8 Example 61.7013.70 5.90 9.80 6.90 MoO₃ 2.00 (Mo/ZrO₂) = 0.25 3 B No. 7-9 Example60.47 13.50 5.80 9.60 6.70 MoO₃ 3.93 (Mo/ZrO₂) = 0.50 3 B No. 7-10Comparative 60.12 13.30 5.70 9.50 6.70 MoO₃ 4.68 (Mo/ZrO₂) = 0.60 38 BExample

TABLE 8 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of GasDevitrifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.8-1 Comparative 70.62 10.00 5.00 7.00 7.00 Ta₂O₅ 0.38 (Ta/ZrO₂) = 0.0332 A Example No. 8-2 Example 70.48 9.90 5.00 7.00 7.00 Ta₂O₅ 0.62(Ta/ZrO₂) = 0.05 3 A No. 8-3 Example 68.86 9.70 4.80 6.80 6.80 Ta₂O₅3.04 (Ta/ZrO₂) = 0.25 0 B No. 8-4 Example 66.80 9.40 4.70 6.60 6.60Ta₂O₅ 5.90 (Ta/ZrO₂) = 0.50 1 B No. 8-5 Comparative 66.10 9.30 4.60 6.506.50 Ta₂O₅ 7.00 (Ta/ZrO₂) = 0.60 34 C Example No. 8-6 Comparative 62.6013.90 6.00 10.00 7.00 Ta₂O₅ 0.50 (Ta/ZrO₂) = 0.04 35 A Example No. 8-7Example 62.58 13.90 6.00 9.90 7.00 Ta₂O₅ 0.62 (Ta/ZrO₂) = 0.05 2 A No.8-8 Example 61.06 13.60 5.80 9.70 6.80 Ta₂O₅ 3.04 (Ta/ZrO₂) = 0.25 2 BNo. 8-9 Example 59.30 13.20 5.60 9.40 6.60 Ta₂O₅ 5.90 (Ta/ZrO₂) = 0.50 1B No. 8-10 Comparative 58.60 13.00 5.60 9.30 6.50 Ta₂O₅ 7.00 (Ta/ZrO₂) =0.60 29 C Example

TABLE 9 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of GasDevitrifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.9-1 Comparative 70.70 9.90 5.00 7.00 7.00 Bi₂O₃ 0.40 (Bi/ZrO₂) = 0.03 27A Example No. 9-2 Example 70.44 9.90 5.00 7.00 7.00 Bi₂O₃ 0.66 (Bi/ZrO₂)= 0.05 2 A No. 9-3 Example 68.70 9.70 4.80 6.80 6.80 Bi₂O₃ 3.20(Bi/ZrO₂) = 0.25 1 B No. 9-4 Example 66.49 9.40 4.70 6.60 6.60 Bi₂O₃6.21 (Bi/ZrO₂) = 0.50 1 B No. 9-5 Comparative 65.74 9.30 4.60 6.50 6.50Bi₂O₃ 7.36 (Bi/ZrO₂) = 0.60 26 C Example No. 9-6 Comparative 62.67 13.906.00 9.90 7.00 Bi₂O₃ 0.53 (Bi/ZiO₂) = 0.04 33 A Example No. 9-7 Example62.54 13.90 6.00 9.90 7.00 Bi₂O₃ 0.66 (Bi/ZrO₂) = 0.05 2 A No. 9-8Example 60.90 13.60 5.80 9.70 6.80 Bi₂O₃ 3.20 (Bi/ZrO₂) = 0.25 0 B No.9-9 Example 59.09 13.10 5.60 9.40 6.60 Bi₂O₃ 6.21 (Bi/ZrO₂) = 0.50 2 BNo. 9-10 Comparative 58.24 13.00 5.60 9.30 6.50 Bi₂O₃ 7.36 (Bi/ZrO₂) =0.60 26 C Example

TABLE 10 The Number SiO₂ Al₂O₃ Li₂O Na₂O ZrO₂ Fining Agent of GasDevitrifi- (% by (% by (% by (% by (% by (% by Bubbles cation mass)mass) mass) mass) mass) Type mass) (molar ratio) (number) Properties No.10-1 Comparative 70.73 10.00 5.00 7.00 7.00 CeO₂ 0.14 ((Ce + Sn)/ZrO₂) =0.03 34 A Example SnO₂ 0.13 No. 10-2 Example 70.55 10.00 5.00 7.00 7.00CeO₂ 0.24 ((Ce + Sn)/ZrO₂) = 0-05 0 A SnO₂ 0.21 No. 10-3 Example 69.469.80 4.90 6.80 6.80 CeO₂ 1.19 ((Ce + Sn)/ZrO₂) = 0.25 0 B SnO₂ 1.05 No.10-4 Example 67.81 9.60 4.80 6.70 6.70 CeO₂ 2.34 ((Ce + Sn)/ZrO₂) = 0.500 B SnO₂ 2.05 No. 10-5 Comparative 67.39 9.50 4.70 6.60 6.60 CeO₂ 2.78((Ce + Sn)/ZrO₂) = 0.60 28 B Example SnO₂ 2.43 No. 10-6 Comparative62.74 13.90 6.00 10.00 7.00 CeO₂ 0.19 ((Ce + Sn)/ZrO₂) = 0.04 27 AExample SnO₂ 0.17 No. 10-7 Example 62.65 13.90 6.00 10.00 7.00 CeO₂ 0.24((Ce + Sn)/ZrO₂) = 0.05 0 A SnO₂ 0.21 No. 10-8 Example 61.56 13.70 5.909.80 6.80 CeO₂ 1.19 ((Ce + Sn)/ZrO₂) = 0.25 0 B SnO₂ 1.05 No. 10-9Example 60.21 13.40 5.70 9.60 6.70 CeO₂ 2.34 ((Ce + Sn)/ZrO₂) = 0.50 0 BSnO₂ 2.05 No. 10-10 Comparative 59.69 13.30 5.70 9.50 6.60 CeO₂ 2.78((Ce + Sn)/ZrO₂) = 0.60 25 B Example SnO₂ 2.43

Each raw material was put into a melting furnace heated at 900° C.-1300°C., followed by melting, clarification, and homogenization by stirring,and then the resulting molten glass was press-molded to prepare a blankmaterial. Thereafter, by inner and outer circumference processing, aswell as grinding and polishing processing, a glass substrate having anouter diameter of 65 mm, an inner diameter of 20 mm, and a thickness of0.635 mm was produced.

With regard to each of the thus-produced glass substrates, the number ofresidual gas bubbles and devitrification properties during melting wereevaluated. The evaluation of the number of residual gas bubbles wasconducted in such a manner that the number of gas bubbles per glasssubstrate was counted with respect to the entire surface of a glasssubstrate by using an optical microscope of a magnification of 50 gasbubbles. The evaluation of the devitrification properties was conductedby judging the numerical value of the difference ΔT (° C.) betweenT_(log η=2.5) (° C.) and T_(L) (° C.) (ΔT=T_(log η=2.5)−T_(L)), where atemperature at which the melting viscosity of a glass satisfies theexpression of log η=2.5 is T_(log η=2.5) (° C.) and the liquid-phasetemperature is T_(L) (° C.). When the relationship 150° C.≦ΔT wassatisfied, the evaluation result was the best (A). When the relationship50° C.≦ΔT<150° C. was satisfied, the evaluation result was good (B).When the relationship ΔT<50° C. was satisfied, the evaluation result wasproblematic (C). Herein, the liquid-phase temperature T_(L) refers to atemperature at which generation of devitrified substances has beenobserved on the surface of or in the interior of a glass after beingkept melting at 1550° C. for two hours followed by being kept in atemperature gradient furnace for ten hours with a temperature gradientand rapidly cooled. Further, T_(log η=2.5) refers to a temperature atwhich equation log η=2.5 was held when the viscosity of a molten glassis determined using a stirring viscometer. The evaluation results eachare collectively shown in Table 1-Table 10.

The evaluation results confirmed that in Examples of the presentinvention in which a polyvalent element functioning as a fining agentmade of an oxide in a glass was contained such that the molar ratio toZrO₂ in the glass components fell in a predetermined range, the numberof residual gas bubbles was remarkably smaller than in ComparativeExamples, and a glass substrate for an information recording medium withsufficiently removed gas bubbles was obtained. Further, when the totalcontent of polyvalent elements was at most 1% by mass with respect tothe total glass components, the devitrification properties wereconfirmed to be most excellent

1. A glass substrate for an information recording medium made ofaluminosilicate glass containing 60% to 75% by mass of SiO₂, 5% to 18%by mass of Al₂O₃, 3% to 10% by mass of Li₂O, 3% to 15% by mass of Na₂O,and 0.5% to 8% by mass of ZrO₂ with respect to whole glass components,and containing neither As (arsenic) element nor Sb (antimony) element,comprising: at least one polyvalent element selected from the groupconsisting of V (vanadium), Mn (manganese), Ni (nickel), Nb (niobium),Mo (molybdenum), Sn (tin), Ce (cerium), Ta (tantalum), and Bi (bismuth),wherein a molar ratio of a whole amount of the comprised polyvalentelement to the ZrO₂ in the glass substrate, which is represented by (thewhole amount of the comprised polyvalent element)/ZrO₂, is within arange of 0.05 to 0.50.
 2. The glass substrate for an informationrecording medium of claim 1, comprising: at least one polyvalent elementselected from the group consisting of V (vanadium), Mn (manganese), Sn(tin), and Ce (cerium).
 3. The glass substrate for an informationrecording medium of claim 1, wherein a total content of the comprisedpolyvalent element is 1% by mass or less with respect to the whole glasscomponents, where each of the polyvalent elements is converted in termsof the following oxides: V₂O₅ for V; MnO₂ for Mn; Ni₂O₅ for Ni; Nb₂O₅for Nb; MoO₃ for Mo; SnO₂ for Sn; CeO₂ for Ce; Ta₂O₅ for Ta; and Bi₂O₃for Bi.
 4. The glass substrate for an information recording medium ofclaim 1, wherein the comprised polyvalent element is added as finingagent made of oxide, hydroxide, or carbonate.
 5. The glass substrate foran information recording medium of claim 1, wherein the glass substratefor an information recording medium is chemically strengthened by ionexchange.
 6. An information recording medium, comprising: a recordinglayer provided on the glass substrate for an information recordingmedium of claim
 1. 7. The glass substrate for an information recordingmedium of claim 2, wherein a total content of the comprised polyvalentelements are 1% by mass or less with respect to the whole glasscomponents, where each of the polyvalent elements is converted in termsof the following oxides: V₂O₅ for V; MnO₂ for Mn; Ni₂O₅ for Ni; Nb₂O₅for Nb; MoO₃ for Mo; SnO₂ for Sn; CeO₂ for Ce; Ta₂O₅ for Ta; and Bi₂O₃for Bi.
 8. The glass substrate for an information recording medium ofclaim 2, wherein the comprised polyvalent elements are added as finingagents made of oxide, hydroxide, or carbonate.